1. Field of the Invention
This invention relates to a method of manufacturing a liquid crystal display device in which liquid crystal is sealed between substrates by using a one drop fill method, and a one drop fill apparatus used for the same.
2. Description of the Related Art
A color liquid crystal display device of an active matrix type has a TFT substrate formed a thin film transistor (TFT) or the like on an insulating substrate, and a CF substrate with a color filter (CF) or the like formed thereon. At a substrate attaching process in a liquid crystal display device manufacturing process, a seal material is applied to the outer peripheral part of either one of the TFT substrate or CF substrate. Next, the two substrates are superimposed and then pressurized and laminated by using a substrate laminating apparatus such as a pressure-heating apparatus or vacuum heating apparatus, thus forming a laminated substrate having a predetermined cell gap width. At a liquid crystal injection step after hardening the seal material, liquid crystal is injected into the cell gap of the laminated substrates by using a vacuum injection technique, and the liquid crystal injection port is sealed.
However, in the vacuum injection technique, it becomes more difficult to evenly inject liquid crystal into the gap as the substrate size increases. Moreover, to facilitate reduction in the cost of liquid crystal panels, simplification of the manufacturing process to improve productivity is demanded. Thus, as a technique for solving these problems, liquid crystal injection using the following one drop fill method is becoming popular. In the one drop fill method, a seal material made of a photosensitive hardening resin or photo and thermo-setting resin is applied in a frame-shape to the outer periphery of one substrate. Next, a predetermined quantity of liquid crystal is dropped on plural parts at predetermined dropping intervals within the frame of the seal material on the substrate. On the other substrate, spherical spacers coated with an adhesive (adhesive spacers) are scattered. Next, the two substrates are carried into a substrate laminating apparatus. One of the substrates is held on a lower plate and the other substrate is held on an upper plate. Next, the upper and lower plates are brought close to each other in a vacuum and the two substrates are laminated to produce a laminated substrate. Next, the atmospheric air is fed into the vacuum chamber to restore the atmospheric pressure, and a cell gap is defined utilizing the difference in pressure between the inside and outside of the laminated substrates. Next, ultraviolet rays (UV rays) are irradiated on the laminated substrates or the laminated substrates are heated after they are irradiated with ultraviolet rays, thus hardening the seal material. Instead of scattering of spherical spacers, pillar spacers made of a resin or the like may be formed on the substrate and the spacer scattering step may be omitted.
Patent Document 1: JP-A-2001-281678
As described above, in the one drop fill method, the substrates on which liquid crystal has been dropped are laminated and then irradiated with UV rays to harden the seal material. Therefore, if the positions where the liquid crystal is dropped are too close to the seal material, the liquid crystal spread by the lamination of the substrates may break the seal material before hardening and may leak out. Moreover, since the components of the seal material before hardening easily elute, if the liquid crystal contacts the seal material before hardening, the seal material components may contaminate and deteriorate the liquid crystal. On the other hand, if the positions where the liquid crystal is dropped are too far from the seal material, the liquid crystal cannot spread sufficiently to the edge of the seal material, generating a bubble area in which the liquid crystal is not injected. If the liquid crystal contaminated and deteriorated by the seal material components or the bubble reaches the display area, an area of uneven display or display defect is generated and the display quality is lowered.